The present invention relates to a boom assembly for a hydrostatically operated trenching machine, and more particularly, to a boom assembly wherein the digging boom is pivotally connected to a casting that is rigidly mounted to the trencher frame.
It is conventional to provide a hydrostatically operated trenching machine having a digging boom which is connected to a tractor for pivotal movement. A digging chain is rotatably mounted on the boom and driven for digging in the ground, and an auger is provided which disperses the spoil that is dug during the trenching operation to the sides of the trench. An example of a trenching machine of the type just described is disclosed and illustrated in U.S. Pat. No. 4,327,508, which is assigned to the assignee of the present invention.
The trenching machine disclosed in U.S. Pat. No. 4,327,508 includes a totally enclosed drive train assembly for the digging chain drive sprocket and spoil dispersing auger. A generally cylindrical boom lift casting is mounted to the tractor frame by a pair of pivot bearings such that the digging boom and boom casting pivot in the trencher frame. A boom lift cylinder is mounted in the trencher frame and attached to the boom lift casting of rotating the boom. The assembly further includes a hydraulic drive motor which is mounted to one end of the boom lift casting and a planetary gearbox which is mounted to the opposite end of the boom lift casing with the planetary gearbox being drivingly connected to the hydraulic drive motor. A digging chain drive sprocket is connected to the planetary gearbox housing to receive the rotational driving force transmitted to the gearbox by the hydraulic motor. Moreover, the planetary gearbox includes a housing for rotatably mounting the auger such that the rotational driving force of the hydraulic motor is transmitted to the auger through the planetary gearbox.
As the boom pivot bushings wear in this known construction, the entire boom assembly may become loose which could result in some misalignment of the drive components. Further, the torque reactions within the drive train assembly are transferred through the boom lift casting and into the boom lift cylinder. These reactions can be substantial when, for example, the digging chain comes in contact with a rock. Thus, there has been a need for an improved digging boom assembly to overcome these disadvantages and undesirable results.